For the testing of digital circuitry it is often desirable to have the capability of injecting test pulses into selected points of the circuit under test. For such purposes it is known to use an external pulser to induce changes of state (high to low, or low to high) at appropriate points in the digital circuit. Logic pulsers are known in the art which provide single pulses and/or a continuous stream of pulses to the circuit under test. However, for many test purposes it is desirable to provide not only single pulses or continuous pulse streams but also repeating bursts of a fixed number of pulses.
To select among the possible output functions of a pulser, it is desirable to have an extremely simple mode select mechanism; preferably mode selection should not be accomplished by a simple mechanism which can be incorporated into a hand-held device, such as are finding wide acceptance in the art. In known devices function selection and control are typically performed by cumbersome switches or even involve instrumentation external to the pulse generator itself.
With the advent of different types of digital circuitry, e.g. DTL, TTL, and CMOS, it is becoming of importance to have a logic pulser which can be operated to compatibly stimulate any of these types. In particular a logic pulser should be capable of generating fast edge pulses to drive CMOS logic at suitable voltages (typically 5-15V), and yet automatically adjusting its output voltage and pulse width to protect DTL and TTL devices.